Fetal distress (including cerebral hypoxia) during labor represents a risk factor for death or severe neurologic complications (e.g., cerebral palsy). More than 4,000,000 babies are born annually in the United States and are candidates for monitoring during labor. Although fetal heart rate monitoring provides an indirect indicator of fetal oxygenation, to date, there are no commercially available monitors that directly monitor the adequacy of fetal cerebral blood flow. Thus, the need for noninvasive measurement of cerebral oxygenation in fetuses is particularly pressing. In this SBIR Phase I application, we propose to develop a fetal interface for a prototype system that we have developed for monitoring cerebral oxygenation in patients with traumatic brain injury. The system will provide accurate, noninvasive measurement of cerebral venous blood oxygen saturation in fetuses during late stage labor through the open anterior fontanelle or through the thin cranial bones. Cerebral venous oxygen saturation, an established monitor in patients with severe traumatic brain injury, provides in a single number an assessment of the ability of cerebral blood flow and cerebral blood oxygen content to meet cerebral oxygen requirements. In our previous works, we described, built and tested in experimental animals, adult volunteers and very-low-birth-weight neonates an optoacoustic device for noninvasive monitoring of cerebral venous oxygen saturation. Our optoacoustic system provides accurate measurement of oxygen saturation (R2 = 0.990), specifically in the superior sagittal sinus, because high (optical) contrast and high (ultrasound) resolution permit direct probing of blood vessels. The specific aims of the proposed project are: 1) to develop for use in fetuses during late stage labor a clinical prototype patient interface that is compatible with our optoacoustic platform; and 2) to test the system in vivo in fetuses during late-stage labor. After implementation of the proposed project, we will build and test a manufacturing-ready prototype and secure 510k clearance from the FDA.